Solid particles can be removed from a gas by introducing the gas tangentially into a cyclone. Separation then takes place between the gas and the solid particles entrained by the gas. The gas leaves the cyclone via the gas outlet at the top of the cyclone. The solid particles are discharged at the bottom of the cyclone.
When the cyclone operates at elevated pressure, problems may arise during the discharge of the solid particles. For discharging the solid particles to a vessel having a lower, usually atmospheric, pressure it is necessary to use a sluice. In that case the solid particles are first collected in a collecting vessel, the solid particles are allowed to flow into the sluice. The pressure in the sluice is then decreased to substantially the pressure in the vessel having a lower pressure. The solid particles are then transferred to the latter vessel. The sluice is thus alternately filled and emptied. This implies that the collecting vessel is also emptied at intervals.
When the solid particles flow from the collecting vessel into the sluice, gas displaced from the sluice flows into the collecting vessel. Since the solid particles may agglomerate in the collecting vessel and form a more or less compact mass, it is desirable that the solid should be shaken loose when the collecting vessel is being emptied. This is preferably performed by creating a slight excess pressure in the sluice in relation to the collecting vessel. When the connection between the sluice and the collecting vessel is opened, a gas stream resulting from said excess pressure will shake loose the solid particles. The excess pressure is preferably up to 5% of the absolute pressure in the collecting vessel.
If no special measures are taken, a quantity of the gas displaced from the sluice by the solid particles enters the cyclone via the solids outlet. This is caused by the excess pressure in the sluice and the velocity at which the gas is displaced from the sluice. Gas flowing into the cyclone via the solids outlet has an unfavorable effect on the operation of the cyclone. The present invention aims at providing a process for removing solid particles from a gas, in which process gas is prevented from entering the cyclone via the solids outlet.